Amino acids, in particular lysine and threonine, are used in animal nutrition, in the foodstuffs industry, in the pharmaceuticals industry and in human medicine.
It is known that these substances are prepared by fermentation of strains of coryneform bacteria, in particular Corynebacterium glutamicum. Because of its great importance, work is constantly being undertaken to improve the preparation processes. Improvements to the processes can relate to fermentation measures, such as e.g. stirring and supply of oxygen, or the composition of the nutrient media, such as e.g. the sugar concentration during the fermentation, or the working up to the product form by e.g. ion exchange chromatography, or the intrinsic output properties of the microorganism itself.
Methods of mutagenesis, selection and mutant selection are used to improve the output properties of these microorganisms. Strains which are resistant to antimetabolites or are auxotrophic for metabolism products of regulatory importance and produce the desired amino acid are obtained in this manner.
Methods of the recombinant DNA technique have also been employed for some years for improving the strain of Corynebacterium strains which produce L-amino acid.